Colloid Cysts of the Third Ventricle comprise 1% of CNS tumors.
These lesions are benign. However, when symptomatic, the outcome may
be fatal if untreated. Complete removal will result in a cure. Colloid
Cysts affect men and women with approximately equal frequency. They
usually become symptomatic from the third to the sixth decade.

ETIOLOGY

The origin of Colloid Cysts has been debated for a long time.
Various different cells have been proposed as the origin of these cysts,
including the incorporation of respiratory and enteric epithelium in the
normal developing Brain. Other possible cells of origin include the
neuroepithelial ependymal lining of the ventricles of the Brain, or the
Choroid Plexus of these ventricles.

Figure 1: The Ventricular System lies entirely within the Central
regions of the Brain. CSF is made in the two Lateral Ventricles
which empties into the centrally located Third Ventricle through
narrow channels - the FORAMEN of MONRO. It is here where Colloid
Cysts form.

SYMPTOMS

The signs and symptoms produced by these lesions are primarily related to
increased intracranial pressure due to Obstructive Hydrocephalus.
The most frequent findings are: headache, change in mental status,
nausea and vomiting, ataxia (balance difficulty), visual disturbance,
emotional lability/affect change (changes in mood/emotional context),
depersonalization, and increased sleepiness. As the Cyst enlarges, it
intermittently obstructs the flow of Cerebrospinal Fluid (CSF
- which is manufactured by the Choroid Plexus within the Ventricles
of the Brain) at the level of the Foramen of Monro (a vital
interconnecting pathway within the Brain's ventricular cavities). With
continued growth, the obstruction becomes complete. This is a true
Neurosurgical emergency demanding surgical treatment, lest death occur
quickly. Colloid Cysts may also cause symptoms by pressure on
adjacent structures, which results in symptoms such as disturbances
in memory, emotion, and personality.

DIAGNOSIS

CT and MRI scans form the basis for diagnosing Colloid
Cysts. They also provide information regarding the presence or absence
of Hydrocephalus. These lesions appear as round or oval masses in the
anterior and superior portion of the Third Ventricle of the
Brain, at the level of the Foramen of Monro. (See Figures 3, 4 & 5
for a case of Acute Obstructive Hydrocephalus resulting from a Colloid
Cyst).

TREAMENT

Surgery

A Colloid Cyst is one of only two medical conditions that can
cause sudden death. SURGICAL REMOVAL CAN BE CURATIVE.

Several different operative techniques are available including
Endoscopic removal of the Cyst, Transcallosal or Transcortical
Transventricular resection of the Cyst, and
Stereotactic Aspiration of the Cyst (See below for a
review of these procedures.)

Since there are no pathognomonic (absolute diagnostic) signs and
symptoms for Colloid Cysts, the correct diagnosis and
treatment depend on a physician's strong clinical sense of suspicion, which
derives from the careful integration of history, neurological examination,
and neuroimaging studies.

Not all patients, in whom a Colloid Cyst is discovered,
require immediate surgical intervention. Observation, without
surgical treatment, may be an option in the patient who does
not have Hydrocephalus and whose symptoms cannot be attributed
to the lesion. If a patient decides not to have this lesion
removed there must be complete patient compliance, ready access to
Neurosurgical attention, and the ability to deal with the knowledge and
implications of the lesion's existence. Nevertheless, in our opinion, A
DECISION NOT TO HAVE THIS LESION REMOVED IS A FLIRTATION WITH DEATH.

Emergency Management

Patients with elevated intracranial pressure and Hydrocephalus
will require urgent surgical therapy. Patients exhibiting acute
deterioration, often require immediate stabilization with a
Ventriculostomy (an operation to place a small tube into one of the
Brain's Lateral Ventricles), to relieve the pressure from the
Hydrocephalus.

Endoscopic Surgery

Endoscopic removal of the Colloid Cyst
has the benefits of potentially being a less invasive procedure
and shorter operative time. The Endoscope is inserted through a
small opening in the Skull and is then advanced through the Brain into the
Ventricular system. Once the Endoscope is maneuvered
into position the Neurosurgeon is able to place small instruments through
the Endoscope allowing for aspiration of the contents followed by removal
of the cyst.

The Endoscope, which has a tiny camera
attached to it, is being held by Dr. Bland. Dr. Lazar is performing
the operation by manipulating micro-surgical instruments inserted
through the Endoscope. Both surgeons are watching a television
monitor which displays the image transmitted from the Endoscope's
camera.

Craniotomy

The Transcortical and Transcallosal approaches involve
performing a small Craniotomy (an opening of the Skull to
gain access to the Brain.) These two approaches differ by virtue of which
Brain structures are crossed to remove the cyst. Essentially, both of these
approaches have the advantage that allow the surgeon direct access to
the Colloid Cyst. The disadvantage is that the
procedure is more invasive and may require a little longer operative
time, compared with the Endoscopic technique.

Figure 7 A (Top Left): Operative Photo during a Right
Transventricular approach to remove a Colloid Cyst. This is a view
of the interior of the Ventricle. The Septum Pellucidum
(Quadrangular Arrow) is bulging because of the obstructed Foramen
of Monro. The Choroid Plexus (Horizontal Arrow) leads to the Foramen
of Monro (Curved Arrow).

Figure 7B (Top Right): The Choroid Plexus has been coagulated in
order to permit visualization and access to the Foramen of Monro
which is filled with tumor (Curved Arrow).

Figure 7C (Bottom Left): The Colloid Cyst (Arrows) is exposed and
isolated within the Foramen of Monro prior to removal.

Figure 7 D (Bottom Right): The Colloid Cyst has been removed
permitting a view THROUGH the Foramen of Monro into the
3rd Ventricle. (Compare this to Figures 7A-C where views
of the Foramen of Monro are restricted.)

Stereotactic Aspiration

Stereotactic approaches can be used for aspiration of
the Colloid Cyst. This involves stereotactically placing a
needle into the Cyst, to remove the fluid. Once the fluid is
removed the size of the Cyst decreases and the pressure on the adjacent
structures decreases. This option is usually not advocated because of a
high risk of refilling of the Cyst with fluid, as well as the
risk for spillage of the contents of the Cyst which can cause
a sterile (non-infectious), inflammatory ventriculitis.

Ventricular Shunt

A Ventricular Shunt is a CSF diversion system. The
"Shunt" is made of Silastic tubing and incorporates a one-way flow
valve mechanism that allows CSF (which is under high pressure within the
Ventricular system) to be diverted to the abdominal cavity from where it is
reabsorbed back into the body's fluid management systems.

This is an alternative method for managing the Hydrocephalus
that occurs in patients with a Colloid Cyst although complete
removal of the Colloid Cyst usually obviates the need for a Shunt to be
placed. However, some patients, even with complete removal of the Cyst,
may still require a Ventricular Shunt in the case of
persistent, symptomatic Hydrocephalus.

There are unusual circumstances where a less invasive procedure may be
required such as in those few patients, who are in very poor medical
condition and are at high risk for an operation to remove the Colloid
Cyst. In these instances, the patient could be treated with only
"shunting" of the obstructed ventricles, to control the increased
intracranial pressure related to the Hydrocephalus. In this situation
the patient becomes entirely reliant upon the continued functioning
of the shunt device (a condition known as "Shunt
Dependent"). In the event of a "Shunt Failure" the patient may
become catastrophically ill requiring emergency Neurosurgical
intervention.